Voltage-nonlinear resistors

ABSTRACT

A voltage-nonlinear resistor has a sintered body of a composition comprising, as a main constituent, zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi2O3), 0.05 to 3.0 mole percent of antimony oxide (Sb2O3) and 0.1 to 3.0 mole percent of manganese fluoride (MnF2). Electrodes are applied to opposite surfaces of the sintered body.

United States Patent [191 Matsuoka et al.

[ VOLTAGE-NONLINEAR RESISTORS,

[75] Inventors: Michio Matsuoka; Mikio Matsuura;

Yoshikazu Kobaynshi; Takeshi v Masuyama, all of Osaka, Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: Feb. 23, 1973 21 Appl. No.: 335,421

[30] Foreign Application Priority Data Mar. 1, 1972 Japan 47-21806 Mar. 1, 1972 Japan 47-21807 Mar. 1, 1972 Japan 47-21808 Mar. 1, 1972 Japan.....'. 47-21809 Mar. 1, 1972 Japan 47-21810 Mar. 1, 1972 Japan 47-21811 Mar. 1, 1972 Japan 47-21812 [52] US. Cl 317/61, 252/518, 338/21 [51] Int. Cl. H0211 3/22 [11 3,806,765 [451 Apr. 23, 1974 [58] Field of Search 317/61, 61.5; 338/20, 21,

[56] References Cited UNITED STATES PATENTS 3,515,947 6/1970 Stetson 317/61 3,642,664 2/1972 Masuyama et a1 252/519 3,663,458 5/1972 Masuyama et al.... 3,693,053 9/1972 Anderson 317/61 X Primary Examiner-Roy N. Envall, Jr. Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [5 7] ABSTRACT A voltage-nonlinear resistor has a sintered body of a composition comprising, as a main constituent, zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (B1 0 0.05 to 3.0 mole per- "cent of antimony oxide (Sb O and 0.1 to 3.0 mole percent of manganese fluoride (MnF Electrodes are applied to opposite surfaces of the sintered body.

6 W9 i}, ra F n-r9 I VOLTAGE-NONLINEAR RESISTORS The invention relates to nonlinear resistors having non-linear ohmic resistance in response to changes in voltage due to the bulk thereof hereinafter called voltage-nonlinear and more particular to varistors, which are for useful elements of lightning arrestors,

comprising zinc oxide, bismuth oxide, antimony where V is the voltage across the resistor, I is the current flowing through the resistor, C is a constant corresponding to the voltage at a given current and exponent n is a numerical value greater than 1. The value of n is calculated by the following equation:

where V, and V are the voltages at given currents I and I respectively. The desired value of C depends upon the kind of application to which the resistor is to be put. it is ordinarily desirable that the value of n be as large as possible since this exponent determines the extent to which the resistors depart from ohmic characteristics. Conveniently, the n-value defined by 1,, [2, V, and V as shown in equation (2) is expressed by /1 for distinguishing it from the n-value calculated by other currents or voltages.

Nonlinear resistors comprising sintered bodies of zinc oxide with or without additives and havingnon-ohmic electrodes applied thereto, have already been disclosed as seen in U.S. Pats. No. 3,496,512, No. 3,570,002 and No. 3,503,029. The nonlinearity of such varistors is attributed to the interface between the sintered body of zinc oxide with or without additives and the silver paint electrode and is controlled mainly be changing the compositions of said sintered body and silver paint electrode. Therefore, it is not easy to control the C-value over a wide range after the sintered body is prepared. Similarly. in varistors comprising germanium or silicon p-n junction diodes. it is ditticult to control the (-ralue over a wide range because the nonlinearity of these varistors is not attributed to the bulk but to the H1 junction. In addition, it is almost impossible for the varistors and germanium or silicon diode varistors have a combination of C-value higher than 100 volts n-value higher than and high surges of resistance tolerable for surge more than 100A.

On the other hand, the silicon carbide varistors have nonlinearity clue to the contacts among the individual grains of silicon carbide bonded together by a ceramic binding material, i.e., due to the bulk, and the C-value is controlled by changing the dimension in the direction in which the current flows through the varistors. In addition, the silicon carbide varistors have high surge resistance which make them useful as elements of lightning arresters. The elements are used usually by connecting them in series with discharging gaps to control the level of the discharging voltage and the follow current. The silicon carbide varistors, however, have a relatively low n-value ranging from 3 to 7 which results in poor suppression of lightning surge or increase in the follow current. Another defect of the arrester including the discharging gaps as components is that it does not respond instantaneously to surge voltage having a very short rise time such as below l,u.s. It is desirable for the arrester to suppress the lightning surge and the follow current to a level as low as possible and respond to surge voltage instantaneously.

There have been known, on the other hand, voltagenonlinear resistors of the bulk type comprising a sintered body of zinc oxide with additives comprising bismuth oxide and antimony oxide and/or manganese oxide, as seen in U.S. Pat. No. 3,663,458. The C- value of these zinc oxide varistors of the bulk type can be controlled by changing the distance between electrodes and have an excellent nonlinear property and an n-value more than 10 in a region of current below 10A/cm For a current more than l0A/cm however, the n-value goes down to a value below 10. The power dissipation for surge energy shows a relatively low value compared with that of the conventional silicon carbide arrester, so that the change rate of C-value exceeds 20 percent after two standard lightning surges of 4 X IOfLS wave with a form having a peak current of 1500A/cm are applied to said zinc oxide varistor 0f the bulk type. There is known another zinc oxide varistor of the bulk type which contains as an additive manganese fluoride as seen in U.S. Pat. No. 3,642,664. This varistor has an excellent nonlinear property, but an essentially weak point as an arrester element is its weakness with respect to a surge pulse. The nonlinear property of the varistor deteriorates easily even for Ap/cm of surge pulse.

An object of the present invention is to provide a voltage-nonlinear resistor having nonlinearity due to the bulk thereof and being characterized by a high nvalue even in a range of current more than IOA/cm.

Another object of the present invention is to provide a voltage-nonlinear resistor having high power dissipation for surge energy.

Another object of the present invention is to provide an arrester characterized by high suppression for a lightning surge and low follow current.

These and other objects of the invention will become apparent upon consideration of the following descrip tion taken together with the accompanying drawing in which FIG. 1 is a partly cross-sectional view through a voltage-nonlinear resistor in accordance with the invention and FIG. 2 and FIG. 3 are partly cross-sectional views through an arrester in accordance with the invention.

Before proceeding with a detailed description of the voltage-nonlinear resistors contemplated by the invention, their construction will be described with reference to FIG. 1 wherein reference character 10 designates, as a whole, a voltage-nonlinear resistor comprising, as its active element, a sintered body having a pair of electrodes 2 and 3 applied to opposite surfaces thereof. Said sintered body 1 is prepared in a manner hereinafter set forth. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3, respectively, by a connection means 4 such as solder or the like.

A voltage-nonlinear resistor according to the inverition comprises a sintered body of a composition comprising, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimocy oxide (Sb O and 0.1 to 3.0 mole percent of manganese fluorideYMnFz and th erem ainder zinc oxide (ZnO) as a main constituent, and electrodes applied to opposite surfaces of said sintered body. Such a voltage-nonlinear resistor has non-ohmic resistance due to the bulk itself. Therefore, its C-value can be changed without impairing the n-value' by changing the distance between said opposite surfaces. According to the invention, said resistor has a high n-value in a region of current more than l0A/cm and high stability with respect to surge pulses.

The highefh-value in a region of current more i536 IOA/cm can be obtained when said sintered body further includes one member selected from the group consisting of 0.1 and 3.0 mole percent of cobalt oxide (C00) and 0.1 to 3.0 mole percent of manganese oxide (MnO).

According to the present invention, the higher nvalue in a region of current more than lOA/cm and the higlir st ability with resaefarsurga ill sesame obtained with said sintered body comprises, as a main constituent, zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi2O 0.05 to 3.0 mole percent of antimony oxide (Sb-20 0.1 to 3.0 mole percent of manganese fluoride (MnFg), 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr O 0.1 to 3.0 mole percent of tin oxide (SnO and 0.1 to 10.0 mole percent of silicon dioxide (SiO According to the present invention, the n-value of the resistor is remarkably improved in a region of current more than l0A/cm and the stability with respect to a surge pulse when said sintered body consists essentially of 99.4 to 72 mole percent of zinc oxide (ZnO) and, as an additive, 0.l to 3.0 mole percent of bismuth oxide (B50 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 .to 3.0 mole percent of manganese fluoride (MnF 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr O and 0.1 to 10.0 mole percent of silicon dioxide (SiO According to the present invention, when at least one voltage-nonlinear resistor consisting essentially of a sintered body of a composition comprising as a main constituent, zinc oxide and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi o 0.05 to 3.0 mole percent of antimony oxide (Sb O and 0.1 to 3.0 mole P n of ma an @9 14; tMrEianQ e ectrode applied to opposite surfaces of said sintered body is used in an arrester as a characteristic element, the resultant arrester produce a lower follow current and has improved suppression and power dissipation with respect to a lightning surge.

According to th'e'prsem invention, when at least one voltage-nonlinear resistor consisting essentially of a sintered body of 99.4 to 72.0 mole percent of zinc oxide (ZnO), 0.1 to 3.0 mole percent of bismuth oxide (Bi- 0 0.05 to 3.0 mole percent of antimony oxide (Sb- 0 0.1 to 3.0 mole percent of manganese fluoride (MB), 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr- 0 and 0.1 to 10.0 mole percent of silicon dioxide (SiO and electrodes applied to opposite surfaces of said sintered body is used as a characteristic element in an arrester, the resultant arrester produces a still further lowered follow current and has further improved supression and power dissipation with respect to a lightning surge.

The sintered body 1 can be prepared by a per se well known ceramic technique. The starting materials in the compositions in the foregoing description are mixed in a wet mill so as to produce homogeneous mixtures. The mixtures are dried and pressed in a mold into desired shapes at a pressure from 50 l(g./cm to 500 Kg./cm The pressed bodies are sintered in air at l000 to l450C for l to 10 hours, and then furnace-cooled to room temperature (about 15C to about 30C). The mixtures can be preliminarily calcined at 700 to 1000C and pulverized for easy fabrication in the subsequent pressing step. The mixture to be pressed can be admixed with a suitable binder such 26 water, polyvinyl alcohol, etc. It is advantageous that the sintered body be lapped on the opposite surfaces by abrasive powder such as silicon carbide having a particle size of 50p. in means diameter to 10p. in mean diameter. The sintered bodies are provided, at the opposite surfaces thereof with electrodes by any available and suitable method such as silver painting, vacuum evaporation or flame spraying of metal such as Al, Zn, Sn etc.

The voltage-nonlinear properties are not affected to any practical extent by the kinds of electrodes used, but are affected by the thickness of the sintered bodies. Particularly, the C-value varies in proportion to the thickness of the sintered bodies, while the n-value is almost independent of the thickness. This surely means that the voltage-nonlinear property is due to the bulk itself, but not to the electrodes.

Lead wires can be attached to the electrodes in a per se conventional manner by using conventional solder. It is convenient to employ a conductive adhesive comprising silver powder and resin in an organic solvent in order to connect the lead wires to the electrodes. Voltage-nonlinear resistors according to this invention have a high stability with respect to temperature and a surge test, which is carried out by applying a lightning surge determined by the J EC (Japanese Electrotechnical Committee)-l56 Standard. The n-value and C-value do not change remarkably after heating cycles and the surge test. It is advantageous for achievement of a high stability with respect to humidity and high surge current that the resultant voltage-nonlinear resistors be embedded in a humidity proof resin such as epoxy resin and phenol resin in a per se well known manner.

When voltage-nonlinear resistors according to this invention are used as to a lightning arrester element, the resultant arrester is improved remarkably with respect to the following current and the suppression property for a lightning surge. FIG. 2 is a crosssectional view of an arrester wherein reference character 20 designates, as a whole, an arrester comprising, one or more voltage-nonlinear resistors according to this invention 11 as elements which are connected in series with one or more discharging gaps 1 2, spring 13 and line terminals 14 and 15, Said arrester elements are enveloped in wet-process porcelain 16. In said arrester the follow current is kept to a level below 1 11A and surge dissipation to a level higher than ZOOOA/cm FIG. 3 is a cross-sectional view of another arrester wherein reference character 30 designates, as a whole, an arrester comprising at least one voltage-nonlinear resistor according to this invention. in the embodiment shown FIG. 3, reference characters identical to those of FIG. 2 have been employed to designate like elements. The arrester o f FTC. 3 has no disefiaiging a s'aniriias'a response time shorter than 0.1 as for high surge having very sharp rise in respect to addition to its excellent properties in follow current and surge dissipation. Presently preferred illustrative embodiments of the invention are as follows.

EXAMPLE 1 Starting material composed of 98.0 mole percent of zinc oxide, 0.5 mole percent of bismuth oxide, 1.0 mole percent of antimony oxide, and 0.5 mole percent of manganese fluoride is mixed in a wet mill for 24 hours.

The mixture is dried and pressed in a mold into discs of 40 mm in diameter and 25 mm thickness at a pressure of 250Kg/cm The pressed bodies are sintered in air at the con ditions shown in Table l, and then furnace-cooled to room temperature. Each sintered body is lapped at the opposite surfaces thereof into the thickness shown in Table 1 by silicon carbide abrasize having a particle size of 30,11 in mean diameter. The opposite surfaces of each sintered body are provided with a spray metallized film of aluminum by a per se well known technique.

1118311531110 characteristics of resultant sintered bodies are shown in Table l, which shows that the C-value varies approximately in proportion to the thickness of the sintered body while the n-value is essentially independent of the thickness. It will be readily realized that the voltage-nonlinear property of each sintered body is attributed to the sintered bodyitself.

TABLE 1. Continued 5 445 15 1200C, 5hr initial 20 1680 14 1350C, lhr 15 1250 14 1350C, 1hr 840 14 1350C, lhr 5 420 14 1350c, lhr initial (20 3600 16 1000C, 10hr 2700 16 1000C, 10hr 10 i800 15 1000C, 10hr 5 900 16 1000C, 10hr EXAMPLE 2 Zinc oxide having incorporated therein bismuth oxide, antimony oxide, and manganese fluoride in 5 the amounts of Table 2 is fabricated into the voltagenonlinear resistors by the same process as that of Example 1. The thickness is mm. The resulting electrical properties are shown in Table 2, in which the values of m and n are the n-values defined 20 between 0.1mA and lmA, and between 100 and 1000A, respectively. The impulse test is carried out by applying 2 impulses of 4 l0us, 10,000A. It can be easily understood that the combined addition of bismuth oxide, antimony oxide, and manganese fluoride as additives produces the high n-values and small change rates.

TABLE 2 Change rates Electrical properties of eiter test; Additives (moi. percent) resultant resistor (percent) 0 (at 0.1- 100 B120; S1320: MIlFz 1 ma 1 ma. 1,000 :1. AC Am Am 0. 05 0. 1 1, 420 12 10 -19 18 -8.1 0. 05 3.0 1, 060 12 11 17 19 7. 2 3. 0 0. l 1, 900 12 11 17 18 7. 3. 0 3. 0 1, 700 12 11 15 17 8. 1 0. 05 0. 1 2, 200 13 12 16 16 6. 3 0.05 3.0 1, 950 13 11 -15 15 7. 5 3.0 0.1 2, 400 11 12 16 -17 6. 8 3.0 3.0 2,160 12 12 1s --18 -0.3 1.0 0. 5 1, 800 15 13 13 14 4. 0

EXAMPLE 3 Zinc oxide with the additives of Table 3 is fabricated into the voltage-nonlinear resistors by the same 1 process as that of Example 1. The electrical properties of the resulting resistors are shown in Table 3. The change rates of C and n values after an impulse test TABLE 1 carried out by same method as that of Examples 2 Thickness C n simmng are also shown in Table 3. it Wlll be readily realized (mm) (at lmA) 0.1-lmA I Condition that the further addition of cobalt oxide or manganese (20) {228 {i 5 oxide results in a higher n-value and smaller change 10 905 is 1200C, 5hr rates that those of Example 2.

TABLE 3 Electrical properties of Change rates after Additives (moi. percent) resultant resistor test (percent) B1203 Sb O; MnF C00 M lme.) ma. 1,0000. AC Ani Am TABLE 3. Continued Electrical properties of Change rates after Additives (mol. percent) resultant resistor test (percent) Am Am C(at 0.1-1 100- B1103 SD20; MnFz C MnO lma.) ma 1,000a.

0 00 00 00000 000000 mmmmmmmmmnmmwmenammmmmuem 1. 1 1M1h1 1 1fl n1 1 L HLLLLLLLLZI LL 10.111000111000105 QKQQQqmomAmQQQQmQmQmQQmO 1100 0105 U O 3 &3 0 3 Q U1001 00511011011001001005 3033OBQmQQQNmQQQmQQQmQmQRTmQQMQWQ 50050000 0 u .o .wwmmm 0 0 0 Q0 mmmmmmmwmem 0 a 0 3 1 aaanrmrakmkanaamm EXAMPLE 5 The resistors of Examples 2, 3, and 4 are tested for stability with respect to temperature and humidity in accordance with methods widely used in testing electron teristics of the resulting resistors are shown in Table 4. It will be easily understood that the further addition ponents parts. The heating cfils'ffika'm of tin oxide, chromium oxide, silicon dioxide or 30 in which said resistors chromium oxide and silicon dioxide results in a higher by repeating times a cycle are kept at 85C ambient temperature for 30 minutes, cooled rapidly to C 5655b? and then kept at such temperature for minutes. The humidity test is carried out at C and 95 n-value and smaner efiaiige ratesthan t Example 3. The change rates of C and n values percent relative humidity for 1000 hrs. Table 5 shows the average change rates of C-value and n-value after an impulse test carried out by same method as 35 that of Example 2 are also shown in Table 4.

TABLE 4 Electrical properties of resultant resistor Change rates after test (percent) 2 a n we 10 0 1 Lmm 1 CW m 1 m S 0 D. C m H S U o mn WM m mm C e .w n Mn M m b s m m 80972770970983971781 914 12112112112112112112m%%%wm122mn% %m%% 19285730503810 947527 700 82000 0 0 000 000 0 0O 0 0 0 0 0 0O $10 4mmwmmwwemwmswwmemmmmmmmh mmme? 1 m n m n m 0 d ma 0.0 0

111555000101555000111555000111555000 0 00 0 0330m0 00 QQQQmQmQmQQQQQQ mQWQmQQQQQQK Ma 55500000 5 000 000 .0000 w .mw .p .pw%mp w w .111333 of resistors after the heating cycle test and the humidity test. It is easily understood that each sample has a small change rate.

h e-" w ?twi ter?a sp ns1 Ex ples 2, 3 and 4 are incorporated in an arrester as shown in FIG. 2 in a series connection of 3 resistors and l discharging gap. The total C-value of said voltage-nonlinear resistors is about 7000V. The impulse test is carried out by applying 2 impulses of 4X 10,us, l500A/cm superposed on AC at 3000V. The follow current of the arrester has the value lower than l .LA as shown in Table 6 and the change rates of electrical properties after the test show same results as for the impulse test of Examples 2, 3 and 4.

TABLE 6 Sample No. Follow-current Example 2 below than lp.A Example 3 below than 0.5;1.A Example 4 below than 0.1;LA

EXAMPLE 7 The voltage-nonlinear resistors according to Exam-- ples 2, 3 and 4 are incorporated in an arrester as shown in F IG. 3 in a series connection of 3 resistors. The total C-value of said resistors is about 7000V. An impulse test was carried out by the same method as that of Example 6. The follow current had the value lower than 1,uA as shown in Table 6 and the change rates of electrical properties after the test showed same results as that of the impulse test in Examples 2, 3 and 4. Another impulse test was carried out by applying an impulse having a value of 0.01 ts rise time. The rise time of current flowing through said arrester was lower than 0.05ps.

What is claimed is:

l. A voltage-nonlinear resistor consisting essentially of a sintered body of a composition comprising, as a main constituent, zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi o 0.05 to 3.0 mole percent of antimony oxide (Sb O and 0.1 to 3.0 mole percent of manganese fluoride (MnF and electrodes applied to opposite surfaces of said sintered body.

' 2. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes one member selected from the group consisting of 0.1 to 3.0 mole percent of cobalt oxide (C00) and 0.1 to 3.0 mole percent of manganese oxide (MnO).

3. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr- 0 0.1 to 3.0 mole percent of tin oxide (SnO and 0.1 to 10.0 mole per cent of silicon dioxide (SiO;).

4. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body consists essentially of 99.4 to 72.0 mole percent of zinc oxide (ZnO), 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 to 3.0 mole percent of manganese fluoride (MB), 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr O and 0.1 to 10.0 mole percent of silicon dioxide (SiO 5. An arrestor comprising at least bn e voltagenonlinear resistor of claim 1 as a characteristic element.

6. An arrester comprising at least one voltagenonlinear resistor of claim 4 as a characteristic element. 

2. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes one member selected from the group consisting of 0.1 to 3.0 mole percent of cobalt oxide (CoO) and 0.1 to 3.0 mole percent of manganese oxide (MnO).
 3. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr2O3), 0.1 to 3.0 mole percent of tin oxide (SnO2) and 0.1 to 10.0 mole percent of silicon dioxide (SiO2).
 4. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body consists essentially of 99.4 to 72.0 mole percent of zinc oxide (ZnO), 0.1 to 3.0 mole percent of bismuth oxide (Bi2O3), 0.05 to 3.0 mole percent of antimony oxide (Sb2O3), 0.1 to 3.0 mole percent of manganese fluoride (MnF2), 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr2O3) and 0.1 to 10.0 mole percent of silicon dioxide (SiO2).
 5. An arrestor comprising at least one voltage-nonlinear resistor of claim 1 as a characteristic element.
 6. An arrester comprising at least one voltage-nonlinear resistor of claim 4 as a characteristic element. 